Method for synchronizing two control devices, and redundantly designed automation system

ABSTRACT

A method for synchronizing a first control device and a second control device of a redundantly structured automation device that controls a technical process is provided. The first control device and the second control device are connected to each other. The first and second devices include functional components which implement the functions that control the technical process. The first control device performs the functions in the functional components for controlling the technical process in cycles, thus creating internal states of the functional components. During control of the technical process by the first control device, information about the internal states of the functional components is transferred, distributed over several cycles, to the second control device. The second control device assigns the transmitted information about the internal states to the functional components. In addition, a corresponding redundantly structured automation device is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2007/060281, filed Sep. 27, 2007 and claims the benefitthereof. The International Application claims the benefits of EuropeanPatent Office application No. 06020610.9 EP filed Sep. 29, 2006, both ofthe applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a method for synchronizing a firstcontrol device and a second control device of a redundantly designedautomation system for controlling a technical process, wherein the firstcontrol device and the second control device are interconnected, eachcontaining a plurality of function blocks by means of which functionsfor controlling the technical process are implemented. The presentinvention also relates to a redundantly designed automation system.

BACKGROUND OF INVENTION

Such a redundantly designed automation system for controlling atechnical process is used in areas of automation engineering in whichheightened requirements are placed on the availability and reliabilityof the automation system. These are areas in which shutdown of the plantcarrying out the technical process would be extremely costly or could behazardous for the personnel involved or the environment. A redundantlydesigned automation system of this kind is also termedhigh-availability. It is employed, for example, in the chemical industryor for operating a power plant. The automation system contains twoseparately operating control devices with which central functions forcontrolling the technical process are redundantly designed. Underfault-free conditions, the two control devices usually execute identicalprograms for controlling the process. These programs contain functionblocks by means of which the functions for controlling the technicalprocess are implemented. Such function blocks are e.g. logic functionssuch as an AND function, arithmetic functions, a counting function, amonitor function with which, for example, a temperature overshoot can bemonitored, etc. The function blocks are concatenated or interconnectedin the program. The programs and their function blocks are cyclicallyand synchronously executed, synchronously meaning that internal statesof the function blocks occurring when the function blocks are executedare identical in the two control devices. In the case of a countingfunction with a counter as the function block, the latter's internalstate is e.g. a counter reading. Only one of the two control devices isactive at any one time, i.e. only the active control device is actuallyactively controlling the technical process via its output control data.The other control device is in a passive state. In order to keep thepassive control device constantly updated with the reading of the activecontrol device, input data is also fed to the passive control deviceprior to the start of each cycle. This input data usually comes fromfield units or other in some cases redundant control devices. Such fieldunits, or field devices, are usually external units or devices such assensors or actuators. In the event of a malfunction in which a faultoccurs in one of the control devices, or when one of the control devicesis undergoing maintenance, operation is switched from the affectedcontrol device to the unaffected control device so that the lattercontinues to control the technical process.

When the fault has been cleared or maintenance is complete, the shutdown control device must be restored to the current reading of thecontrol device currently controlling the technical process. For thispurpose, all the internal states of the function blocks of the controldevice currently controlling the process must also be assigned to thefunction blocks of the shut down control device. To do this, control ofthe process is usually interrupted at the start of a particular cycle.During said interruption, all the information about the internal statesis transmitted all at once to the shut down control device by thecontrol device that has been controlling the process prior to theinterruption. As it takes a certain period of time to transmit theinformation about the internal states, the program with which thetechnical process is controlled by the control devices disadvantageouslycannot be executed during this period of time. In order to minimize thistime, the information about the internal states of all the functionblocks is first packed, i.e. aligned together, written to a specialmemory area and then the packed data is copied to the shut down controldevice. The start addresses of the information about the internal statesassigned to the individual function blocks must be known to the shutdown control device. Only thus can it assign the transmitted informationabout the internal states to its function blocks. In this process,incorrect assignment of the information about the internal states to thefunction blocks can easily occur.

SUMMARY OF INVENTION

The object of the present invention is to enable two devices of anautomation system to be reliably synchronized in a technically simplemanner.

This object is achieved with regard to the method and with regard to thedevice by the independent claims. Advantageous embodiments of theinvention can be inferred from the dependent claims.

In the method according to the invention, the first control devicecyclically executes its function blocks for controlling the technicalprocess, thereby generating internal states of the function blocks.While the technical process is being controlled by the first controldevice, information about the internal states of its function blocks istransmitted, distributed over several cycles, to the second controldevice. The second control device additionally assigns the transmittedinformation about the internal states to its function blocks.

The inventive redundantly designed automation system for controlling atechnical process has a first control device and a second control devicewhich are interconnected, each containing a plurality of function blocksby means of which functions for controlling the technical process areimplemented. For their synchronization, the first control device and thesecond control device are designed such that the first control devicecyclically executes its function blocks for controlling the technicalprocess, the function blocks thereby generating internal states. Inaddition, while controlling the technical process, the first controldevice transmits information about the internal states of its functionblocks, distributed over several cycles, to the second control device.The second control device assigns the transmitted information about theinternal states to its function blocks.

According to the present invention, the two control devices aresynchronized over a plurality of cycles. The information about theinternal states is not fed to the second control device all at once, butin a plurality of transfer operations. This enables sufficiently smallamounts of data with information about the internal states to betransmitted from the first to the second control device in the differentcycles. The first control device can transmit these small amounts ofdata in the cycles as well as controlling the technical process, i.e.for the cyclical execution of the different function blocks. It is notnecessary for the controlling of the process by the control devices tobe interrupted. The data with the information about the internal statescan be successively transmitted to the second control device. The amountof data transmitted from the first to the second control device in oneof the cycles in addition to controlling the process can advantageouslydepend on how much capacity the first control device requires forcontrolling the process and possibly for other tasks that are given ahigher priority than synchronization with the second control device. Inparticular, the control devices represent runtime environments for thefunction blocks for executing configurable and freely programmable open-and closed-loop control tasks. The function blocks of the first andsecond control device are in particular of identical form. Internalstates of function blocks are, in particular, states or values possessedby the function blocks. The internal states can in particular alsoinclude instance information or data containing old values from previouscycles which are summed or integrated over a plurality of cycles. If theinternal states of the function blocks of identical form are identicalin the two control devices, then the two control devices are operatingsynchronously.

In an advantageous embodiment of the invention, the information aboutthe internal states of the function blocks of the first control deviceis transmitted to the second control device prior to execution of thefunction blocks in the plurality of cycles. This ensures in particularuniform loading of the two control devices. The second control devicecan therefore assign said transmitted information to the associatedfunction blocks. These function blocks with the assigned, currentinternal states can be executed at the start of the next cycle.

In another particularly advantageous embodiment, the information aboutthe internal states of the function blocks of the first control devicecan be transmitted to the second control device together with input datafrom field units and/or other control devices. This enables informationand inputs to be transmitted to the second control device particularlyefficiently. Control of the transmission of the required information andinputs can be implemented in a simple manner.

The second control device preferably assigns the transmitted informationabout the internal states, distributed over the plurality of cycles, toits function blocks. This ensures in particular uniform loading of thesecond control device.

Particularly preferably, the information about the internal states ofthe function blocks is transmitted function block by function block.This ensures optimum organization and control of the transmissionprocess. It also enables the second control device to assign thetransmitted information block by block to its function blocks, therebyenabling the assignment process to be simplified. Although, the numberof function blocks for which the information about their internal statesis transmitted is in particular irrelevant here, it must advantageouslybe ensured that detrimental effects on the cyclical execution of thefunction blocks due to synchronization are avoided.

In addition, the plurality of function blocks are preferably executed inthe plurality of cycles in a predefined runtime sequence and theinformation about the internal states of the function blocks istransmitted in said predefined runtime sequence. The enables thetransmission process to be controlled in a particularly efficientmanner.

Particularly preferably, an input value of an input of the functionblocks of the first control device is additionally transmitted to thesecond control device, and the second control device assigns saidtransmitted input value to an input of one of its function blocks. Thisensured particularly reliable and rapid synchronization of the twocontrol devices.

Particularly preferably, the transmitted input value is assigned by thesecond control device to such an input of one of its function blockswhich is connected to an output of another of its function blocks whichranks lower in the predefined sequence than the one of its functionblocks, already transmitted information about internal states havingbeen assigned to the one of its function blocks and no information aboutinternal states having been assigned to the other of its functionblocks. This enables reliable synchronization to be ensured especiallyin the case of feedback function blocks. Once synchronized, a functionblock of the second control device, to which function block the updatedinternal states have been assigned, therefore remains in synchronismwith the corresponding function block of the first control device evenif lower order function blocks are not yet synchronized.

The respective function blocks are preferably assigned their own memoryareas. The internal state information assigned to the respectivefunction blocks is stored in the memory areas allocated to therespective function blocks, thereby enabling erroneous overwriting ofinformation by other function blocks to be prevented. This also allowsparticularly free and reliable programming of the function blocks andruntime environments. The separate memory areas are protected inparticular by an operating system of the control devices so that pointerovershoots are prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will now be explained in greater detailwith reference to examples and exemplary embodiments and theaccompanying drawings in which:

FIG. 1 schematically illustrates a redundantly designed automationsystem according to the invention,

FIG. 2 schematically illustrates a first and second control device ofthe redundantly designed automation system with non-feedback functionblocks and

FIG. 3 schematically illustrates the first and second control devicewith feedback function blocks.

DETAILED DESCRIPTION OF INVENTION

In the Figures, identical or functionally identical elements are—unlessotherwise stated—provided with the same reference characters.

FIG. 1 shows a schematic drawing of an inventive redundantly designedautomation system 1 for controlling a technical process which is carriedout in a plant. Such a plant can be, for example, a power plant or achemical plant. The automation system 1 contains a first control device2 which has a memory 3. In the memory 3 a control program is storedwhich is executed as sequencing control for the controlling of theprocess by the first control device 2 and in which compiled functions,parameters and other data are contained. The control program contains aplurality of function blocks with which particular sub-functionalitiesfor controlling the process by means of the automation system can beexecuted. Said function blocks are interconnected in a particular wayand exchange data depending on the interconnection. When the controlprogram is executed by the first control device 2, the function blocksassume particular internal states. The memory 3 is subdivided intodifferent memory areas 4 a-4 n. Said memory areas 4 a-4 n are allocatedto the different function blocks of the control program, each of thefunction blocks being assigned its own memory area 4 a-4 n which it canaccess. Information concerning the internal states of the functionblocks and other data is stored in the memory areas 4 a-4 n.

The automation system 1 also contains a second control device 5. Thedesign of the second control device 5 essentially corresponds to that ofthe first control device 2. The second control device 5 contains amemory 6 in which the same control program is stored as in the memory 3.Correspondingly, the memory 6 also contains the plurality of functionblocks. The function blocks of the second control device 5 correspond tothose of the first control device 2. The function blocks of the twocontrol devices 2, 5 are of identical form. The memory 6 is subdividedinto different memory areas 7 a-7 n. Said memory areas 7 a-7 n areallocated to the different function blocks of the control programcontained in the second control device 5, each of the function blocksbeing allocated its own memory area 7 a-7 n which it can access.Information concerning the internal states of the function blocks andother data is stored in the memory areas 7 a-7 n. In addition to the twocontrol devices 2, 5 the automation system can have further, possiblyidentically designed control devices.

The two control devices 2, 5 represent runtime environments with whichopen- and closed-loop control tasks for controlling the technicalprocess can be carried out. The automation system is redundantlydesigned by means of the two control devices 2, 5. During normaloperation, the two control devices 2, 5 are identically configured andexecute the identical programs contained in them in parallel, thefunction blocks being executed cyclically. During normal operation, thefunction blocks of the two control devices 2, 5 assume identical statesat each point in time. The two control devices 2, 5 operatesynchronously and are therefore able to control the process. Theautomation system 1 controls the two control devices 2, 5 such that oneof them is switched active. Active in this context means that thecontrol device switched active is actually controlling the process, i.e.output data generated by it is fed out to the plant to be controlled.The other control device is then switched passive, i.e. the passivecontrol device executes the control program, but the output data whichit generates in doing so is not forwarded to the plant. In the exemplaryembodiment according to FIG. 1, the first control device 2 and thesecond control device 5 are connected to a switch 8 via which either anoutput of the first control device 2 or an output of the second controldevice 5 can be connected to an output 9 of the automation system 1. Theautomation system 1 is connected via the output 9 to the plant to becontrolled.

The first control device 2 and the second control device 5 areinterconnected via a communication line 10. The two control devices 2, 5can exchange data with one another via said communication line 10. Inparticular, the two control devices 2, 5 can transmit information aboutthe internal states of their respective function blocks to the othercontrol device 2, 5 via the communication line 10, thereby enabling theautomation system 1 to keep its two control devices 2, 5 in synchronism.

The communication line 10 is also used to synchronize the two controldevices 2, 5 should one of the control devices 2, 5 have to be shutdown, e.g. in the event of a fault or for necessary maintenance, etc. Insuch a case, only one of the two control devices 2, 5 executes thecontrol program. The internal states of the function blocks of theother, shut down control device do not then coincide with the internalstates of the function blocks of the control device continuing tooperate normally, even when the fault has been repaired or maintenanceis complete. To re-synchronize the two control devices in order totransfer the internal states of the normally operating control device tothe shut down control device, information about the internal states canbe transmitted via the communication line 10 to the other controldevice.

The latter then stores the transmitted information in the memory areasof its memory. If one of the two control devices 2, 5 has been shutdown, the current internal states of the undisconnected, normallyoperating control device are inventively transmitted incrementally,distributed over several cycles of execution of the function blocks, viathe communication line 10 to the disconnected control device.

The automation system 1 has an input 11 via which it is connected tofield devices, such as sensors and actuators, and other automation orcontrol devices. At the input 11, the automation system 1 receivessignals and data transmitted from these units and devices which are fedto the two control devices 2, 5. This takes place in each case prior tothe start of the cycles for executing the function blocks.

FIG. 2 schematically illustrates the first control device 2 and secondcontrol device 5 of the redundantly designed automation system 1. Insimplified form, the first control device 2 here has three functionblocks FB1, FB2 and FB3 which are interconnected. The first controldevice 2 also has an input 12 where it receives input data from fielddevices and/or other control devices or automation systems. Foroutputting data, an output 13 of the first control device 2 is connectedto the field devices and/or the other control devices or automationsystems. It is also connected to the switch 8. The input 12 is connectedto an input of the function block FB1 and to an input of the functionblock FB3. An output of the function block FB1 is connected to theoutput 13, and another output of the function block FB1 is connected toan input of the function block FB2. An output of the function block FB2is connected to another input of the function block FB3. The functionblocks FB1, FB2 and FB3 are here interconnected in series and withoutfeedback. In this context, feedback means that an output of a subsequentfunction block in the execution sequence of the function blocks FB1,FB2, FB3 is routed to the input of a previous function block.

The second control device 5 is of analogous design to the first controldevice 2. The second control device 2 therefore has three functionblocks FB1′, FB2′ and FB3′ which are interconnected. The second controldevice 5 has an input 14 where it receives input data from field devicesand/or other control devices or automation systems. Said input data canalso be transmitted from the first control device 2 to the secondcontrol device 5 via the communication line 10. For outputting data, anoutput 15 of the second control device 5 is connected to the fielddevices and/or the other control devices or automation systems. It isalso connected to the switch 8. The input 14 is connected to an input ofthe function block FB1′ and to an input of the function block FB3′. Anoutput of the function block FB1′ is connected to the output 15, andanother output of the function block FB1′ is connected to an input ofthe function block FB2′. An output of the function block FB2′ isconnected to another input of the function block FB3′. The functionblocks FB1′, FB2′ and FB3′ are here interconnected in series and withoutfeedback.

The first control device 2 is here the active control device whichcontrols the technical process. The second control device 5 is switchedpassive and has been shut down, e.g. for a number of hours, due to afault which has occurred. During normal operation of the first controldevice 2 for controlling the process, the function blocks FB1, FB2, FB3are sequentially and cyclically executed, said function blocks FB1, FB2,FB3 assuming internal states which change in each cycle executed.

Due to the fact that the second control device 5 has been shut down, andtherefore its function blocks FB1′, FB2′, FB3′ have not been executed,their internal states are not up to date. By incrementally updating theinternal states of the function blocks FB1′, FB2′, FB3′, the latter aresynchronized with the function blocks FB1, FB2, FB3, proceeding here inthe cyclical processing or execution sequence.

In the present example, prior to the first cycle the input data from thefield devices and/or the other control devices or automation systems istransmitted from the first control device 2 to the second control device5 via the communication line 10. Information about the internal state ofthe function block FB1 is additionally transmitted from the firstcontrol device 2 to the second control device 5 via the communicationline 10 prior to the first cycle. This information about the internalstate is then assigned to the function block FB1′ by the second controldevice 5, whereupon the first cycle then starts in the two controldevices 2, 5, the function blocks FB1 and FB1′ being executed. As theinternal states of the two function blocks FB1 and FB1′ have beenpre-synchronized and the same input data is fed to the two functionblocks FB1 and FB1′, the outputs of the two function blocks FB1 and FB1′or their output data are identical after the first cycle. As the inputdata for the two function blocks FB1 and FB1′ is always identical evenin subsequent cycles, it is also not asynchronous in these subsequentcycles. With identical input data, the internal states of the twofunction blocks FB1 and FB1′ will also arise identically in the future.The function blocks FB1 and FB1′ no longer need to be synchronized insubsequent cycles.

Prior to a second cycle, in addition to the input data, informationabout the internal state of the function block FB2 is also transmittedfrom the first control device 2 to the second control device 5 via thecommunication line 10. Said transmitted information about the internalstate is then assigned to the function block FB2′ by the second controldevice 5, whereupon the second cycle then starts in the two controldevices 2, 5, the function blocks FB2 and FB2′ being executed. As theinternal states of the two function blocks FB2 and FB2′ arepre-synchronized and identical input data is fed to the inputs of thetwo function blocks FB2 and FB2′, the outputs of the two function blocksFB2 and FB2′ or their output data is identical after the second cycle.The two function blocks FB2 and FB2′ also remain synchronous insubsequent cycles. With identical input data of the two control devices2, 5 and pre-synchronized function blocks FB1 and FB1′, the internalstates of the two function blocks FB2 and FB2′ will also ariseidentically in the future. The function blocks FB2 and FB2′ no longerneed to be synchronized in subsequent cycles.

The same applies to the synchronizing of the function blocks FB3 andFB3′ in a subsequent third cycle in which information about the internalstate of the function block FB3 is transmitted from the first controldevice 2 via the communication line 10 to the second control device 5and assigned by the latter to the function block FB3′. After the thirdcycle, all the function blocks of the first control device 2 and secondcontrol device 5, and therefore the two control devices themselves, aresynchronized. The second control device 5 is therefore able to assumecontrol of the technical process. The information transmitted by thefirst control device 2 about the internal states of its function blocksFB1, FB2, FB3 is stored by the second control device 5 in the memoryareas 7 a-7 n allocated to the function blocks FB1′, FB2′, FB3′.

FIG. 3 shows another schematic drawing of the first control device 2 andsecond control device 5 of the redundantly designed automation system 1.Although the design of the control devices 2, 5 is largely analogous tothat of the control devices in the example in FIG. 2, theinterconnections of the function blocks FB1 and FB2 and FB1′ and FB2′are different. In the present example, feedback connections are present.An output of the function block FB2 is connected to an input of thefunction block FB1 and, correspondingly, an output of the function blockFB2′ is connected to an input of the function block FB1′. For successivesynchronizing of the function blocks of the two control devices 2, 5 theproblem therefore arises that, in spite of transmission and assignmentof information about the internal state of the function block FB1 to thefunction block FB1′, the input data fed to the inputs of the functionblocks FB1 and FB1′ is different because of the feedback and thedifferent internal states of the two function blocks FB2 and FB2′. Afterthe first cycle, the two function blocks FB1 and FB1′ are thereforeagain asynchronous.

In order to avoid this, for synchronizing the function blocks, inaddition to the input data from the field devices and/or the othercontrol devices or automation systems as well as the information aboutthe internal state of one of the function blocks FB1, FB2, FB3, inputvalues for the inputs of the function blocks FB1′, FB2′, FB3′ are alsotransmitted from the first control device 2 to the second control device5 via the communication line 10 which are connected via a feedbackconnection to outputs of a lower order function block in the runtime orexecution sequence. In the example in FIG. 3, input values of thefunction block FB1 input connected to the function block FB2 output aretherefore transmitted. These transmitted input values are then assignedby the second control device 5 to the function block FB1′ inputconnected to the function block FB2′ output. In this way, the twocontrol devices 2, 5 can be synchronized in a simple manner even in thecase of feedback in the interconnection of the function blocks.

It is also possible for the input values for the function blocks of theshut down control device 5 always to be transmitted, and in addition tothe information about the internal states of the active control device2. Synchronization can be advantageously optimized in the case offeedback by only transmitting input values for such inputs of alreadysynchronized function blocks, said inputs being connected via a feedbackconnection to a function block that has not yet been synchronized.

The invention described can also be advantageously used when individualfunction blocks are not executed in each cycle. Even in this case, theexecution cycle is repeated after a particular number of basic cycles.

Completely object-oriented programmed control devices or runtimeenvironments can be synchronized with components as function blocks forwhich data and internal states are encapsulated and accesses are onlypossible via defined interfaces. In such a case, the function blocksprovide interfaces by means of which the control device or runtimeenvironment can read out the synchronization data and transmit andassign it to the function block to be synchronized.

The invention claimed is:
 1. A method for synchronizing a first controldevice and a second control device of a redundantly designed automationsystem controlling a technical process, comprising: providing aplurality of function blocks which implement a plurality of functionsfor controlling the technical process, the plurality of function blockseach provided to the first and second control devices; cyclicallyexecuting the plurality of function blocks of the first control devicewhich controls the technical process, thereby generating an internalstate for each function block; transmitting, over a plurality of cycles,information including the internal state of each function block of thefirst control device to the second control device while the technicalprocess is being controlled by the first control device, thetransmitting during each of the plurality of cycles including only aportion of all the internal states; assigning transmitted informationabout the internal state of each function block of the first controldevice to a corresponding function block of the second control device,wherein the first control device and the second control device areinterconnected, wherein an input value of an input of the plurality offunction blocks of the first control device is transmitted to the secondcontrol device, wherein the second control device assigns a transmittedinput value to an input of one of the plurality of function blocks ofthe second device, wherein the second control device assigns thetransmitted input value to an input of a first function block of thesecond control device, wherein the input is connected to an output of asecond function block of the second control device that is of a lowerorder than the first function block of the second control device in apredefined runtime sequence, and wherein the first function block hasalready been assigned information and the second function block has notbeen assigned information.
 2. The method as claimed in claim 1, whereinthe information is transmitted to the second control device in theplurality of cycles prior to a start of an execution of the plurality offunction blocks.
 3. The method as claimed in claim 1, wherein thetransmitted information further includes an input data from a field unitand/or a different control device.
 4. The method as claimed in claim 1,wherein the second control device assigns, distributed over theplurality of cycles, the transmitted information to each correspondingfunction block.
 5. The method as claimed in claim 1, wherein theinformation is transmitted one function block at a time.
 6. The methodas claimed in claim 1, wherein the plurality of function blocks areexecuted in the plurality of cycles in a predefined runtime sequence andthe information is transmitted in the predefined runtime sequence. 7.The method as claimed in claim 1, wherein each function block isallocated a memory area which comprises the internal state informationassigned to the respective function block.
 8. The method as claimed inclaim 1, wherein the first control device and the second control deviceare connected to a switch that controls which device is an active deviceand is controlling the technical process.
 9. A redundantly designedautomation system controlling a technical process, comprising: a firstcontrol device; a second control device interconnected to the firstcontrol device; a plurality of first function blocks for the firstcontrol device; a plurality of second function blocks for the secondcontrol device; a first internal state information for each functionblock of the first control device; and a second internal stateinformation for each function block of the second control device,wherein the plurality of function blocks implement a functionality thatcontrols the technical process, wherein the first control device and thesecond control device are configured for a synchronization, wherein thefirst control device cyclically executes a plurality of first functionblocks for controlling the technical process, thereby generating theinternal state of each function block, wherein, while the technicalprocess is being controlled, the first control device transmits,distributed over a plurality of cycles, the first internal stateinformation to the second control device, whereby only a portion offirst internal state information is transmitted in each cycle, whereinthe second control device assigns the transmitted first internal stateinformation to a corresponding function block of the second controldevice, wherein an input value of an input of the plurality of firstfunction blocks of the first control device is transmitted to the secondcontrol device, wherein the second control device assigns thetransmitted input value to an input of one of the plurality of secondfunction blocks of the second device, wherein the second control deviceassigns the transmitted input value to an input of a first functionblock of the second control device, wherein the input is connected to anoutput of a second function block of the second control device that isof a lower order than the first function block of the second controldevice in a predefined runtime sequence, and wherein the first functionblock having already been assigned information and the second functionblock having been assigned no information.
 10. The system as claimed inclaim 9, wherein the first internal state information is transmitted tothe second control device in the plurality of cycles prior to a start ofan execution of the plurality of function blocks.
 11. The system asclaimed in claim 9, wherein the transmitted first internal stateinformation further includes an input data from a field unit and/or adifferent control device.
 12. The system as claimed in claim 9, whereinthe second control device assigns, distributed over the plurality ofcycles, the transmitted first internal state information to eachcorresponding function block.
 13. The system as claimed in claim 9,wherein the first internal state information is transmitted one functionblock at a time.
 14. The system as claimed in claim 9, wherein theplurality of function blocks are executed in the plurality of cycles ina predefined runtime sequence and the first internal state informationis transmitted in the predefined runtime sequence.
 15. The system asclaimed in claim 9, wherein each function block is allocated a memoryarea which comprises the internal state information assigned to therespective function block.
 16. The system as claimed in claim 9, whereinthe first control device and the second control device are connected toa switch that controls which device is an active device and iscontrolling the technical process.